This process relates generally to a chemical, electrochemical method for production of metallic lead and/or zinc and other metals from materials, e.g., ores, including high carbonate ores, containing them usually in the form of their sulfides. The new process avoids conventional environmental and technological disadvantages.
Primarily, lead and zinc ores consist of their respective sulfides, galena and sphalerite, along with minor quantities of oxidation products, oxides, hydroxides, silicates and carbonates and, in the case of lead, the sulfate anglesite. Complex assemblages of the lead-zinc minerals are common due both to physical and chemical reasons, and the presence of carbonate minerals within and surrounding these deposits is not an infrequent occurrence.
Often separation of the sulfide minerals from gangue components and from each other is not satisfactorily achievable by physical and mechanical methods such as application of gravity separation and flotation technologies. In many instances, mineral grain sizes are far too small for such operations, and intergrowth of dissimilar grains within each other are frequently noticed. Separations by such techniques are further complicated by substitution of one metal cation for a portion of another in a given mineral lattice as, for example, iron for zinc forming a mineral species known as marmitite. The presence of copper levels far above solubility capabilities within sphalerite mineral crystals has also been observed.
Conventionally, the lead and zinc ores are concentrated and/or separated by using physical or mechanical methods such as flotation or gravity separation techniques and subsequently roasted with elimination of the contained sulfur as oxidic gas. The roasted concentrates are then reduced to their respective metals by high temperature reduction techniques or by electro-deposition after dissolution in spent electrolyte.
Roasting of sulfide containing concentrates generally means that the contained sulfur is contained in product sulfuric acid or eliminated as a by-product, such as calcium sulfate if air quality regulations and standards are to be met. The disposal of large amounts of either of these materials may present additional problems both economically and environmentally.
Additionally, separation of sulfide minerals from gangue components and from each other is often not satisfactorily accomplished by these physical or mechanical methods. In many cases, mineral grain sizes are too small for such operations and complex inner growths of dissimilar grain structures within each other further complicate the situation. Separations by such methods are further hindered by the substitution of other metal cations into portions of the metal lattice normally reserved for such ions as zinc.
Feedstock chemical purity for lead and zinc roaster concentrates is important for reasons of operational performance and metal loss considerations. Severe penalties are generally imposed for contamination as, for example, by the presence of the other metal or iron.
In commonly assigned U.S. Pat. No. 3,986,943, a chemical process for recovery of metal values from antimony, zinc and/or lead ores and ore concentrates by reaction with a solution containing hydrochloric acid is disclosed. In this process, the leaching step is conducted under atmospheric boiling conditions and the hydrogen sulfide evolved is separately oxidized to elemental sulfur utilizing ferric chloride containing solutions.
Hydrometallurgical process technology covering production of copper from chalcopyrite and other copper-containing materials utilizing ferric chloride solutions is disclosed in commonly assigned U.S. Pat. Nos. 3,785,944 and 3,879,272. In both patents, copper-containing materials are oxidized using ferric chloride-containing solutions producing soluble cupric chloride and elemental sulfur. Cupric chloride is then reacted with additional elemental sulfur. Copper values are recovered from solution by electrodeposition, and regeneration of the ferric chloride is achieved by oxidation using oxygen or an oxygen-containing gas such as air with concurrent purge of excess iron from the leach solution. The effect of combining the ferric chloride oxidation and solution regeneration with an advantageous reduction in iron content of the process solution is specifically noted in U.S. Pat. No. 3,879,272.
A hydrometallurgical process for recovery of antimony from stibnite and other antimony-containing materials by reaction with ferric chloride in an aqueous solution is disclosed in commonly assigned U.S. Pat. No. 3,986,943. In this process, antimony-containing materials are reacted with ferric chloride solution production antimony (III) chloride and elemental sulfur. Antimony metal is recovered by electrodeposition at the cathode of a diaphragm equipped electrolytic cell with ferric chloride regeneration being simultaneously achieved in the anolyte compartment.
Moreover, the deliberate treatment of carbonate minerals such as limestone, dolomite and ankerite with chloride-containing solutions whose active ingredients include ferric chloride or hydrochloric acid has generally been avoided in the past because of reactions resulting in precipitation of the iron values and neutralization of the acid. Accordingly, recovery of metal values from ores containing large amounts of carbonates, has been technologically and economically unfeasible heretofore.
Consequently, large tonnage, relatively high grade deposits of lead-zinc containing ores, especially those wherein the gangue minerals include large amounts of carbonates, cannot by known technology be economically separated from the sulfidic metal values.
The following U.S. Pat. Nos. disclose technology related to that of this invention: 1,251,485, 1,435,891, 1,441,063, 1,456,798, 3,929,597, 1,069,498, 1,173,467, 3,743,501 and 3,973,949.